I I. The glutei muscles.

FIGURE 2.

A, B, C, D, H, I. The same parts as in Fig. 1.

E. The accelerator urinae muscle.

F F. Right and left erector penis muscle.

G G. Right and left transverse muscle.

Plate 51

Figure 2 Figure 1

COMMENTARY ON PLATES 52 & 53.

THE SURGICAL DISSECTION OF THE DEEP STRUCTURES OF THE MALE PERINAEUM.

THE LATERAL OPERATION OF LITHOTOMY.

The urethra, at its membranous part, M, Fig. 1, Plate 53, which commences behind the bulb, perforates the centre of the deep perinaeal fascia, E E, at about an inch and a half in front of F, the anus. The anterior layer of the fascia is continued forwards over the bulb, whilst the posterior layer is reflected backwards over the prostate gland.

Behind the deep perinaeal fascia, the anterior fibres of K, the levator ani muscle, arise from either side of the pubic symphysis posteriorly, and descend obliquely down wards and forwards, to be inserted into the sides of N N, the rectum above the anus. These fibres of the muscle, and the lower border of the fascia which covers them, lie immediately in front of the prostate, C C, Fig. 2, Plate 53, and must necessarily be divided in the operation of lithotomy. Previously to disturb­ing the lower end of the rectum from its natural posi­tion in the perinaeum, its close relation to the prostate and base of the bladder should be noticed. While the anus remains connected with the deep perinaeal fascia in front, the fibres of the levator ani muscle of the left side may be divided; and by now inserting the finger between them and the rectum, the left lobe of the prostate can be felt in apposition with the forepart of the bowel, an inch or two above the anus. It is owing to this connexion between these parts that the lithoto­mist has to depress the bowel, lest it be wounded, while the prostate is being incised. If either the bowel or the bladder, or both together, be over-dis­tended, they are brought into closer apposition, and the rectum is consequently more exposed to danger during the latter stages of the operation. The prostate being in contact with the rectum, the surgeon is enabled to examine by the touch, per anum, the state of the gland. If the prostate be diseased and irregularly enlarged, the urethra, which passes through it, becomes, in general, so distorted, that the surgeon, after passing the catheter along the urethra as far as the prostate, will find it necessary to guide the point of the instrument into the bladder, by the finger intro­duced into the bowel. The middle or third lobe of the prostate being enlarged, bends the prostatic part of the urethra upwards. But when either of the lateral lobes is enlarged, the urethra becomes bent towards the opposite side.

By dividing the levator ani muscle on both sides of the rectum, F, Fig. 2, Plate 53, and detaching and depressing this from the perinaeal centre, the prostate, C C, and base of the bladder, P, are brought into view. The pelvic fascia may be now felt reflected from the inner surface of the levator ani muscle to the bladder at a level corresponding with the base of the prostate, and the neck of the bladder in front, and the vesiculae seminales, N N, laterally. In this manner the pelvic fascia serves to insulate the perinaeal space from the pelvic cavity. The prostate occupies the centre of the perinaeum. If the perinaeum were to be penetrated at a point midway between the bulb of the urethra and the anus, and to the depth of two inches straight backwards, the instrument would transfix the apex of the gland. Its left lobe lies directly under the middle of the line of incision which the lithotomist makes through the surface; a fibrous membrane forms a capsule for the gland, and renders its surface tough and unyielding, but its proper substance is friable, and may be lacerated or dilated with ease, after having partly incised its fibrous envelope. The membranous part of the urethra, M, Fig. 2, Plate 53, enters the apex of the prostate, and traverses this part in a line, nearer to the upper than to the under surface; and that portion of the canal which the gland surrounds, is named prostatic. The prostate is separated from the pudic artery by the levator ani muscle, and from the artery of the bulb, by the deep perinaeal fascia and the muscular fibres enclosed between its two layers.